ISLAMABAD, Pakistan — Pakistan’s ambassador to the United States resigned Tuesday over a scandal that has exposed the ongoing power struggle between the civilian government and a military that directs from the shadows — one that threatened to further destabilize President Asif Ali Zardari’s shaky administration.

The departure of Husain Haqqani removed an envoy known in Washington as a Zardari confidant and an articulate spokesman for civilian rule — attributes that earned him the deep distrust of Pakistan’s powerful military. That tension was crystallized by the swirling controversy, which centers on a Pakistani American businessman’s claim that Haqqani orchestrated a memo asking for U.S. help in diminishing the army’s power after the U.S. raid in May that killed Osama bin Laden in Pakistan.

Haqqani has denied involvement with the memo, which was sent to Adm. Mike Mullen, then the chairman of the Joint Chiefs of Staff, and Mullen has said he ignored the missive. But Pakistan’s generals are said to be outraged, and opposition parties have questioned whether Zardari authorized the memo, which some observers say amounted to treason.

Pakistani officials said the resignation is likely to remove that pressure. But some analysts said that whatever the truth about the document, the uproar has cemented the military’s supreme position — the opposite of what it appeared to be seeking.

“The takeaway from this is that the civilians look suspect and the army looks like the one institution that has Pakistan’s best interests at heart,” said Cyril Almeida, a columnist for the English-language newspaper Dawn. “Anything that diminishes the civilians by definition strengthens the army.”

Pakistan’s ambassador to the United States, Husain Haqqani, has resigned amidst a scandal that underlines tension between Pakistan’s civilian government and its military. (Gerald Herbert/AP)

On Wednesday, Pakistan appointed Sherry Rehman, a former magazine editor and information minister, as the new ambassador to the United States, the Associated Press reported.

Prime Minister Yousuf Raza Gilani said Tuesday that he asked Haqqani to resign so that an investigation could be carried out “fairly, objectively and without bias.” Haqqani, in an e-mail, said he quit to quell a “meaningless controversy.”

“To me Pakistan and Pakistan’s democracy are far more important than any artificially created crisis over an insignificant memo written by a self-centred businessman,” said Haqqani, who flew to Pakistan on Sunday to face questions from civilian and military leaders.

The State Department, while watching the events in Islamabad, appeared to be staying out of a situation in which, in its view, any U.S. involvement would have only negative repercussions. The Obama administration wanted the matter settled before it could interfere with larger concerns about Pakistan’s cooperation in the Afghan war, said U.S. officials who declined to discuss the sensitive diplomatic matter publicly.

The officials questioned whether allowing Mullen — who was close to Gen. Ashfaq Parvez Kayani, Pakistan’s army chief — to become such a prominent point man for the administration had skewed the bilateral relationship toward the military and indirectly contributed to the memo controversy. Because businessman Mansoor Ijaz sent his memo to Mullen, U.S. diplomats were unaware of the situation until it erupted in Pakistan last month. The memo was e-mailed by former national security adviser James L. Jones, whom Ijaz enlisted for the task.

Asked about Haqqani’s resignation, State Department spokeswoman Victoria Nuland said that she was “not going to get into an internal Pakistani issue” and that the Obama administration had received no official notification of his removal.

Senate Foreign Relations Committee Chairman John F. Kerry (D-Mass.), who had worked closely with Haqqani, said in a statement he was “sorry” for the resignation and called Haqqani “a strong advocate for his country and the Pakistani people . . . [whose] wisdom and insights will be missed here in Washington as we continue to work through the ups and downs of our relationship.”

Haqqani’s resignation did little to clarify the provenance of the memo, which asked for help in forestalling a military coup. The matter first surfaced last month in a Financial Times column by Ijaz, who said he had delivered the memo on the instructions of a senior Pakistani diplomat. The column argued that the United States needed to rein in a Pakistani spy branch long alleged to nurture jihadist groups.

In recent days, Ijaz has identified Haqqani as the diplomat and released transcripts of extensive cellphone conversations that he said the two had had as they conceived the memo, which was not signed. Among other things, the government investigation is supposed to examine the authenticity of those messages.

Haqqani supporters have questioned Ijaz’s credibility and suggested that the scandal is an elaborate setup by Pakistani intelligence. They point to Ijaz’s statement that he recently discussed the scandal with Lt. Gen. Ahmad Shuja Pasha in London — the chief of the agency Ijaz criticized in his column.

“It was a conspiracy,” said Fozia Wahab, a senior member of Zardari’s ruling party.

Others said the memo fit the pattern of the civilian government, which has frequently been at odds with the military but has been unwilling to stand up to it publicly.

“He could not have been sacked if there was not enough evidence,” Zafar Hilaly, a former diplomat, said on a talk show on the Express 24-7 news channel.

Haqqani, a former journalist and professor, has been at the center of previous civil-military tussles. In 2009, Pakistani critics accused him of “inserting” clauses that conditioned a multibillion-dollar U.S. assistance package on civilian control over the military, drawing condemnation from the Pakistani army. And after a CIA contractor fatally shot two men in Pakistan this year, Pakistani intelligence leaked figures it said showed the Pakistani Embassy in Washington was giving out scores of visas to Americans without proper oversight. Haqqani denied that, saying visa numbers had remained steady.

Staff writer Karen DeYoung in Washington and special correspondent Shaiq Hussain in Islamabad contributed to this report.

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